两个同源重组血友病家系的基因诊断

Genetic diagnosis of two haemophilia families with recombination

目的探讨特殊血友病家系的基因诊断。方法通过FⅧ基因内含子22倒位及内含子1倒位的直接检测与遗传连锁分析的间接诊断相结合对1个血友病A（HA）家系进行基因诊断；采用核酸直接测序法对FⅨ各外显子及其侧翼序列进行检测，并联合FⅨ基因相关的6个微卫星（STR）位点对1个血友病B（HB）家系进行基因诊断。结果HA家系先证者为FⅧ内含子1倒位阳性，家系中要求做携带者诊断的女性成员为内含子1倒位携带者；而FⅧ基因内外8个多态性位点遗传连锁分析证实该女性成员发生同源染色体重组。HB家系先证者除7号外显子测序未成功外，其余部分均未找到突变，家系中要求做携带者与产前诊断的女性，其羊水细胞经直接核酸测序未找到突变，利用FⅨ相关的6个STR位点进行遗传连锁分析发现该女性有染色体同源重组现象存在，胎儿为正常男性。结论在应用间接诊断方法进行HA和HB的携带者及产前基因诊断时，要考虑到染色体同源重组现象的发生可能导致误诊与漏诊的情况。在中国人群中应该开发更多的FⅧ和FⅨ分子中信息量大的多态性位点，以提高HA和HB的携带者及产前诊断的准确率。

Objective To make genetic diagnosis in two haemophilia families with recombination. Methods For hemophilia A （HA） family, screening of the F Ⅷ intron 22 and intron 1 inversion mutations was employed to identify the mutation. Linkage analysis with 8 polymorphic markers was adopted in the pedigree. For hemophilia B（HB） family, DNA sequencing of all coding regions of FⅨ gene was used to detect the mutation directly. The multifluorescent PCR method employing six b]X related STR was adopted in linkage analysis. Results In the HA family,the proband was positive in inversion 1 detection and the relative female was inversion 1 carrier. But linkage analysis with polymorphic markers showed contrary resuhs. Some markers certified that the female inherited the disease chromosome of the family while the others showed contrary results. In the HB family, it was unsuccessful in sequencing the exon 7 of the FⅨ gene in the proband and there was no mutation found in the other parts. The relative female and her amniocyte DNA were successful in sequencing the whole FⅨ gene and no mutation was detected. The linkage analysis of the family showed contrary resuhs. Recombination occured in these two families. Conclusions Although the linkage analysis is convenient and effective in carrier and prenatal diagnosis of hemophilia families. The recombination risk shouldn＇t be neglected especially when the polymorphic markers give inconsistent information for linkage analysis. It is necessary to find some high informative markers intragenic or on the telomeric side to the gene in order to prevent the risk of recombination.